<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>
    <style>
      .box {
        display: flex;
        justify-content: center;
        align-items: center;
        width: 200px;
        height: 200px;
        border: 1px solid green;
      }

      .son {
        display: flex;
        justify-content: center;
        align-items: center;
        width: 80px;
        height: 80px;
        background-color: red;
      }
    </style>
  </head>
  <body>
    <div class="box">
      <div class="son">哈哈哈</div>
    </div>
  </body>
</html>
